Hydraulic engineering installations

ABSTRACT

A marine foundation in a pool is provided by placing a liquid impermeable sheet on the bed of the pool and locating a drain below the sheet. Then, by applying suction force to the drain, a pressure differential is set up whereby the sheet is sealed to the bed and the adjacent bed material consolidates to effectively form a solid mass embedded below and sealed to the sheet. This action affords a large capability for lateral shearing stresses. In use, anchorages, dam-form barriers, storage tanks, and other structures can be tied to the sheet.

United States Patent [191 Schofield 1 Jan. 15, 1974 HYDRAULIC ENGINEERING 3,599,433 8/1971 Murata 61/36 INSTALLATIONS 2,615,307 10/1952 Kje1lman.... 61/11 3,537,267 11/1970 Webb 61/1 X [75] Inventor: Andrew Noel Schofield, Didsbury, 3 73 3 9 9 gloverm 6] /1 England 3,438,204 4/1969 Cleary 61/1 [73] Assignee: National Research Development Corporafion, LOndOfl, England Primary Examiner.lacob Shapiro [22] Filed: Sept 17, 1971 Att0rneyCushman et a1.

[21] Appl. No.: 181,414

[57] ABSTRACT [30] Foreign Apphcatlmf P nomy Data A marine foundation in a pool is provided by placing Sept. 18, Great Bl'ltaln a per e She on he b of e p nd Sept. 18, 1970 Great Br ta n 44,590/70 locating a drain below the Sheet. Then by pp y g Sept. 18, 1970 Great Brltam 44,591/70 suction force to the drain a pressure differential is set up whereby the sheet is sealed to the bed and the adjag% g cent bed material consolidates to effectively form a i h 46 7 solid mass embedded below and sealed to, the sheet. 1 o This action affords a large capability for lateral shearing stresses. In use, anchorages, dam-form barriers,

t t k th b t' t References Cited zhcgrfipe an s and 0 er structures can e red 0 the UNITED STATES PATENTS 1,987,626 1 1935 Klie 61/36 10 Claims, 9 Drawin Figures PAIENTEDJANI 5 IHM 3,785,158

SHEU 2 BF 3 PATENTED 1 51974 3,785,158

SHEET 3 [IF 3 HYDRAULIC ENGINEERING INSTALLATIONS This invention concerns hydraulic foundations and the formation thereof on the bed of a pool, the term pool being intended to embrace any liquid zone, be it within the sea, a river, a lake, sewage treatment works, and so on.

In order to maintain the difference of liquid surface level between a high level pool and an adjacent low level pool it is necessary to generate shearing stress across the base of the relevant intervening barrier between the pools and also to provide a seal between the barrier and the adjacent bed surface of the pools. Similar requirements can also arise with hydraulic foundations for other purposes, such as anchorages in the sea forming a single level pool. In any event, existing practice for providing such foundations commonly involves the provision of massive structures, at least in terms of dimensions, together with the difficulties of construction that this can be expected to bring in a hydraulic context. 1

An object of the present invention is to provide an improved form of hydraulic foundation which reduces the difficulties associated with existing practice According to one aspect of the present invention there is provided a hydraulic foundation in a pool, comprising a liquid impermeable sheet sealing member disposed on the bed surface of the pool, and liquid drain means located beneath said sealing member.

In another aspect the present invention provides a method of forming a hydraulic foundation in a pool, which comprises locating liquid drain means in or on the bed surface of the pool, disposing a liquid impermeable sheet sealing member on the bed surface and above the drain means, securing said sealing member against movement with any natural liquid movement in the pool, and actively applying, at least temporarily, a suction force to said drain means.

In either aspect of the invention, the sealing member should be substantially inextensible or linked with rigid anchorage elements located in the bed therebelow.

The application of suction force according to this method creates a pressure difference between that applied to the sealing member from above by the pool liquid and that below the sealing element where liquid is drawn into the drain means, and this pressure difference causes the sealing member to seal on to the bed surface and provide a large capability for frictional shearing stresses between surface on the one hand and the member or the associated rigid anchorage elements therebelow on the other hand. In some circumstances, such as where the foundation is associated with adjacent high and low level pools, there can be an inherent pressure difference which serves to apply a suction force to the drain means. In such circumstances it may be possible to terminate active application of suction force following an initial period during which the foundation is established. This possibility, together with oth ers, such as association of a foundation according to the invention with marine barriers, will be clarified by the following more detailed description of theinvention which is given by way of example with reference to the accompanying drawings.

In the drawings:

FIG. 1 illustrates one embodiment of a foundation according to the invention,

FIGS. 2 and 3 respectively illustrate, in schematic side elevation and cross-sectional views, another such foundation in association with a submersible storage tank,

FIGS. 4, 5 and 6 similarly illustrate, in side elevations, foundations in association with flexible barriers, and

FIG. 7 illustrates a further embodiment of a foundation according to the invention.

FIG. 1 shows a typical site for marine anchorage where the bed of the relevant pool 10 may be composed of soil 1] and/or rock 12. If there is soil it may be necessary to insert drains 13 by screwing, jacking or jetting pipes into the soil in order to accelerate drainage under the pressures that will become effective. This then allows soil penetration means, such as earth screws, to be used as effective securement for other members in the foundation. If there is a soft muddy bed surface which is likely to cause clogging of drainage it may be appropriate to place a filter layer 14, such as of paper, on the bed surface. Where rock prevents entry of earth screws or other penetration means, it may be desirable to place strong grillage -plates 15 on the bed surface, at least over any exposed rock. Where a large flow of water may occur through rock fissures, or where seepage forces in soil may cause new fissures, it maybe necessary to grout these fissures.

The earth-screws and grillage-plates may have attachment points 16 for beams 17 which are assembled to form a linkage of rigid anchorage elements over the bed surface. Through this linkage the concentrated tension of the anchorage become distributed over what will be a drained foundation area. Once the linkage is constructed all spaces may be filled in with sand or gravel forming a mound 18 of smooth outline which may be drained.

The mound 18 and the bed surface to some distance therearound are then covered by a liquid impermeable sheet 19 which may conveniently be of butyl rubber. The edge of this sheet is weighted or buried to prevent it from being lifted by currents in the pool.

At various points in the sheet there are sealed joints ,20 which may be formed with screws, nuts and/or washers applying mechanical pressures and with sealing tape and/or mastic to ensure that when tension is applied above the joint it is transmitted rigid anchorage elements below the joint without any passage of water through the joint. 1

These joints can be used to secure slabs 21, such as of concrete armour plate, above the sheet to secure the same against natural movements in the pool and also to protect the sheet against damage by trailing anchors and such like. When suitable rocks 22 are available, these can be heaped above the mound for the same purpose. Alternatively, both the sealing of the mound and protection of the seal can be effected by layers of bitumous or asphaltic material.

From a generally central one of the joints 20 which is connected to the beams 17, an anchor chain 23 rises through the pool to a buoy 24. There is a drainage opening 25 in the sheet 19 through which water can be drained from the mound 18 up a pipe 26 by means of a pump forming part of a pump/compressor 27 located on the buoy. The purpose of pumping is to reduce the water pressure in the drained mound 18 to a value below that in the surrounding pool and so to exert an effective pressure on and bind the mound, the rigid anchorage elements and adjacent bed into an effectively solid mass within the overall bed structure with the sheet sealed and adhered to this mass.

On first pumping from the mound, relatively large flows of water will occur, and it may be convenient during an initial period to have the pump operating continuously on the buoy, sucking water right up to the sea surface and discharging it into the sea.

However, by making the impermeable sheet extend to a sufficient distance around the anchorage it can be ensured that after a time the flow of water will decrease to a slow steady seepage. It is then convenient to make use of a seepage drainage vessel 28, held at an approximate depth D below te upper surface of the pool, into which the slow steady seepage can drain under the action of the pressure of the pool over the sheet. It is necessary for this action that the free space in the vessel 28 be at a lesser pressure than that over the sheet and this is attained by connecting the vessel to atmospheric pressure by way of a vent valve 29 in the pipe 26 above the pool upper surface. At the same time it is necessary that the pipe 26 can be disconnected from the pump and this is possible by means of a valve 30.

In the seepage drainage vessel there may be electrical contacts arranged so that when the water surface therein rises to a certain level a light above the buoy is seen to flash intermittently, or some other equivalent signal is given. In any event, at this signal, the seepage water may then be blown out of the vessel by operation of another valve 31 (shown in detail to the left of FIG. 1

As a preliminary to operation of valve 31, the vent valve 29 is closed, the valve 30 is opened and the pump/compressor 27 is changed over to a compressor function to blow compressed air into the pipe 26. The air pressure above the water in the seepage drainage vessel then rises. Below the seepage vessel is a small reservoir 32 with an entrapped bubble of air. Rise in pressure in the seepage drainage vessel causes a small flow of water down to the reservoir 32 and this flow then closes a ball valve 33 forming part of the valve 31 below the seepage drainage vessel.

The end of the pipe 26 is secured to the seepage vessel in a sealed manner, but between the ball valve 33 and the seepage drainage vessel there are small perforations 34 in the pipe that stems from the seepage drainage vessel. Around these perforations is a length of soft rubber or similar valve tube 35. When the air and water pressures in the seepage drainage vessel rise above the water pressure in the surrounding pool the seepage water is blown out through the perforations 34 into the pool. When bubbles are seen rising through the sea the compressed air supply is cut off at valve 30 and the air vent 29 again opened to atmospheric pressure.

With a seepage drainage arrangement such as just described, if the area of the drained mound is A square metres and if the difference of head between the water within the drained mound (up to the seepage drainage reservoir) and the water in the surrounding sea is D metres, then the vertical anchorage force must not at any time exceed AD tonnes (taking the weight of water as l tonne per cubic metre).

On first pumping from the drained mound there will be pore water pressures in the soil at all depths d metres below the drained mound that correspond to the head of water in the pool rather than to the newly imposed reduced head of water in the drained mound. if the buoyant weight of soil is 'y tonnes per cubic metre and if, at some time after new installation, there is a difference of head y between the pore water in the soil at some depth d and the water in the overlying pool then at that time the vertical anchorage force must not exeeed A('y yd) tonnes, where this calculation is made for the most critical depth d. To ensure that data are available for these calculations, large foundation installations must have appropriate pore pressure and settlement observation systems; small installations must have an adequate factor of safety.

In the case of soft soil pool bed surfaces, where large total settlements can be expected, soil settlement within the depth of penetration of the earth screws can cause relative movement of material and members within the mound and it is important to provide an adequate depth of sand or gravel covering the rigid anchorage element structure to ensure that no part of this structure is effectively exposed to puncture the impermeable sheet.

Also, when earth screws or equivalent penetration means are used, it will normally be desirable that these be mutually spaced over the pool bed at no greater distances than the attained depth of penetration.

Conveniently foundations and associates such as just described can be used to hold down large floating flexible underseas storage bags grouped to form oil storage installations. Similar anchorages may also be used to hold oil pipelines and oil process plants undersea. The available anchorage forces can be made large by increasing the drained area A and/or the effective pressure difference (head D). A similar anchorage may be made for descent to the abyssal zone where an appropriate umbrella mechanism can spread out the impermeable sheet: such an anchorage can then be used to anchor a floating vessel of large excess buoyancy fixed in mid-ocean. The anchorage can also carry large horizontal forces such as act on off-shore drilling outfits in storms, provided that at that time a vertical force about five times as large as the horizontal force is effective on an appropriately designed mound and foundation linkage.

One such application is shown by FIGS. 2 and 3 which show a submersible storage tank as may be used for the off-shore storage of crude oil.

The tank 40 of FIGS. 2 and 3 has a central hollow cavity 41 at its base defined by a circular wall 42. The well 41 A well 43 of smaller cross-sectional area than the cavity communicates with and extends upwardly from the cavity to the top of the tank. The upper end of the well will extend or be connected, such as by conduits to buoys, so that even when the tank is wholly submerged with its bottom adjacent the sea bed 44, the well is in communication with atmosphere.

The tank may be filled or emptied through upper valve means 45 located at the top of the tank, and lower valve means 47 located near the bottom of the tank allow flooding of the tank with sea water.

A flexible annular sheet 48 which may suitably be made of a butyl rubber is provided with a collar 49 at its inner circumference. The collar 49 stands within the inner wall 42 of the tank and is sealed between the inner wall and a tubular sealing member 50.

A plurality of concentric toroidal bags 51 are bonded to the annular sheet 48 and connected to the bottom of the tank. These toroidal bags may be filled initially with air to augment the buoyancy of the installation to enable it to be floated to a desired location, whereafter air may then be pumped out of the toroidal bags and replaced by grouting, mud or sand or other suitable ballast material.

When the upper and lower valve means 45 and 47 in the tank are opened to allow sea water to enter the tank, the installation will sink so that the tank bottom is brought adjacent to the sea bed. The flexible sheet 48 will then mould itself to the surface of the sea bed.

Pumping means are associated with the well 43 and cavity 41 to drain the water contained therein and to supply the cavity with air at atmospheric pressure. The area 52 of the sea bed directly beneath the cavity will then be at atmospheric pressure and a pressure differential will be created between the underside of the flexible sheet 48 and the upper side of this sheet which will be supporting a column of water equivalent to the depth of the sea. Thus there will be a net downward pressure on the sheet 48 near to the collar 49 proportional to the depth of the sea at that point.

This drainage action is similar to that of the embodiment of FIG. 1 and can be enhanced by the provision of sand and gravel and/or drainage pipes below the sheet 48 as denoted in chain line at 53.

In any event, after initial drainage of the cavity 41, there will clearly be some seepage of water under the sheet 48 through the material of the sea bed towards the area 52, and so the pumping means is kept operative as far as is necessary to keep the well 41 substantially free of water, thus maintaining a pressure gradient radially of the annular sheet so that the water always exerts a downward force on the sheet 48, keeping it secured to the sea bed.

The sea level may rise above the upper surface of the tank either permanently or during passage of a long wave over the tank. However, if the height of the drainage cavity is small compared with that of the well, the tank full of buoyant oil with conntinue to press down against the sea bed, provided that the ratio between the tankless-cavity cross sectional area and the tanklesswell cross-sectional area exceeds the ratio between the specific gravities of sea water and oil. The oil, when pumped into thetank through the upper valve means, will float on top of the water in the tank and displace as much water as is appropriate through the lower valve means. Conversely, when the oil is subsequently drawn off through upper valve means, sea water will be drawn in through the lower valve means. Similar techniques are equally appropriate to storage of other water immiscible liquids.

Reference has also been made to association of the presently proposed foundations with barriers between pools of different level. In fact the foundations find particular application with flexible forms of barriers since the barrier can be formed as an effective extension of the associated foundation sheet member. Moreover, such barriers can be employed in many practical applications, such as for tidal surge control and coastal defence, coffer dams and land reclamation, locks and weirs, and so on.

One such flexible barrier arrangement is schematically illustrated in FIG. 4 in which the foundation sheet is indicated at 60 with rigid anchorage elements and drains 61 below. The sheet 60 is upwardly extended from one end to form a barrier 62 which is supported at its upper edge by a float 63 to separate a high level pool 64 and a low level pool 65. In order to maintain this disposition the upper edge of the barrier is connected to the rigid anchorage elements towards the further end of the foundation sheet by tie lines 66. Then all lateral force in the arrangement is transferred as tension through the barrier and its tie lines to be held by friction between the foundation sheet and the adjacent pool bed 67.

FIG. 5 shows a similar arrangements employing the same reference numerals where appropriate, but in which the upper edge of the barrier is supported by rigid props 68 which can be connected to an extension 69 of the foundation sheet. In this case the tie lines are held by frictions in the foundation sheet.

FIG. 6 shows yet another similar arrangement, but in which the barrier loops back to join the remote end of i I the foundation sheet and so form a tubular barrier 70 which can be inflated with water or other fluid. The sheet is linked to the rigid anchorage elements in the region of this joint.

It will be noted that the foundations of FIGS. 4 to 6 show the use of drain pipes extending along the bed surface in a relatively flat rather than a significantly mounded structure. The former is preferred for use with foundations for extensive installations such as barriers, although a mounded arrangement is suitable for less extensive installations such as single point anchorages.

In any event, the flatter foundation structure conveniently can secure a strong scour-resisting structure above the sheet. Such a structure is shown in FIG. 7 in which the bed surface is shown at 80, the foundation sheet at 81 and rigid drain pipes at 82 therebclow in sand and gravel. The sheet is secured and protected by blocks 83 thereover and, to extend the protection where the sheet does not overlie the drains due to the incidence of rocks 84, say, a flexible mesh 85 such as of torpedo netting is interposed between the sheet and blocks. This mesh is connected to the blocks by use of shackles or other fixings 86. Similar fixings can be used to connect the drains by way of sealed joints 87 through the sheet, and such fixings can also be used for anchoring tie lines. The interstices of the structure above the sheet can also be filled with sand, grave] or other suitable material 88.

One remaining point which has arisen during further development of the present foundations, and which should be mentioned, is the possibility of cracks developing. Since a pressure gradient exists during establish ment of the foundation by the promotion of drainage there will be a consolidation of bed material and coarser added material such as gravel. This consolidation can lead to the development of cracks which will tend to lead towards the drainage elements and reduce the spread of drainage action below the sheet. Accordingly it may be desirable to apply grouting material to inhibit this effect. The grouting material should be chosen to fill any cracks which develop without impeding the drainage action. This does not represent a contradiction in requirements: for example, F ulbent 570 (Fullers Earth Union Limited) has been found to flow over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto;

blocks of weighting material located over said sealing member;

said blocks being linked with said sealing member by way of sealed jointed fixed with said member.

2. A structure according to claim 1 wherein relatively large discrete members of said drain means below said sealing member are linked thereto by way of said sealed joints.

3. A load-restraining structure in a pool comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, said foundation including a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto;

blocks of weighting material located over said sealing member;

a flexible mesh-form assembly disposed over said sealing member and below said blocks, which assembly is linked with said blocks.

4. A structure according to claim 1 wherein the interstices between said blocks, and between said blocks and said sealing member, are filled with particulate or mastic material.

5. A load-restraining structure in a pool comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, said foundation including a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto;

in combination with said load-restraining means comprising a flexible sheet barrier serving as an upward extension of said sealing member from one and thereof, means to support the upper edge of said barrier adjacent the upper surface of said pool,

and tension means extending between the upper edge of said barrier and the remote end of said sealing member to transfer force therebetween.

6. A structure combination according to claim 5 wherein said tension means comprises a yet further sheet extension between said sealing member and barrier to define therewith an inflatable tubular structure.

7. A load-restraining structure in a pool of liquid comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, which region is below the liquid of said pool, said foundation including as an active force-dispersing constituent thereof a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and

a super-structure above said foundation, including load-restraining means connected with said sealing member to apply load-restraining force thereto.

8. A structure according to claim 7, said loadrestraining means comprising with a submersible fluid storage tank having a central well depending therethrough to open at the bottom of the tank, and wherein said sealing member is of annular form having an upstanding collar at its inner periphery which is sealingly secured around the wall of said well.

9. A structure according to claim 7 wherein said drain means comprises a zone of particulate material extending laterally adjacent said sealing member, which zone has a plurality of rigid anchorage elements embedded therein in dispersed manner and linked with said sealing member.

10. A method of securing a load-restraining structure in a pool, which method comprises: forming a hydraulic foundation by locating liquid drain means in a region of the bed of said pool which region is below the liquid of said pool, disposing a liquid-tight flexible sheet member over the bed surface of said region, and actively applying at least temporarily a suction force to said drain means to consolidate the bed material of said region; and locating a superstructure above said foundation which superstructure includes load-restraining means connected with said sealing sheet to apply load force to said sheet for dispersal therethrough by generation of shearing stress between said sheet and the bed material of said region. 

1. A load-restraining structure in a pool comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, said foundation including a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto; blocks of weighting material located over said sealing member; said blocks being linked with said sealing member by way of sealed joints fixed with said member.
 2. A structure according to claim 1 wherein relatively large discrete members of said drain means below said sealing member are linked thereto by way of said sealed joints.
 3. A load-restraining structure in a pool comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, said foundation including a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto; blocks of weighting material located over said sealing member; a flexible mesh-form assembly disposed over said sealing member and below said blocks, which assembly is linked with said blocks.
 4. A structure according to claim 1 wherein the interstices between said blocks, and between said blocks and said sealing member, are filled with particulate or mastic material.
 5. A load-restraining structure in a pool comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, said foundation including a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and load-restraining means connected with said sealing member to apply load-restraining force thereto; a flexible sheet barrier serving as an upward extension of said sealing member from one and thereof, means to support the upper edge of saiD barrier adjacent the upper surface of said pool, and tension means extending between the upper edge of said barrier and the remote end of said sealing member to transfer force therebetween.
 6. A structure combination according to claim 5 wherein said tension means comprises a yet further sheet extension between said sealing member and barrier to define therewith an inflatable tubular structure.
 7. A load-restraining structure in a pool of liquid comprising: a hydraulic load-force-dispersing foundation in a region of the bed of said pool, which region is below the liquid of said pool, said foundation including as an active force-dispersing constituent thereof a liquid-tight flexible sheet sealing member disposed over the surface of said region to generate shearing stress therewith, and liquid drain means disposed in and operating to consolidate said region below said sealing member; and a super-structure above said foundation, including load-restraining means connected with said sealing member to apply load-restraining force thereto.
 8. A structure according to claim 7, said load-restraining means comprising with a submersible fluid storage tank having a central well depending therethrough to open at the bottom of the tank, and wherein said sealing member is of annular form having an upstanding collar at its inner periphery which is sealingly secured around the wall of said well.
 9. A structure according to claim 7 wherein said drain means comprises a zone of particulate material extending laterally adjacent said sealing member, which zone has a plurality of rigid anchorage elements embedded therein in dispersed manner and linked with said sealing member.
 10. A method of securing a load-restraining structure in a pool, which method comprises: forming a hydraulic foundation by locating liquid drain means in a region of the bed of said pool which region is below the liquid of said pool, disposing a liquid-tight flexible sheet member over the bed surface of said region, and actively applying at least temporarily a suction force to said drain means to consolidate the bed material of said region; and locating a superstructure above said foundation which superstructure includes load-restraining means connected with said sealing sheet to apply load force to said sheet for dispersal therethrough by generation of shearing stress between said sheet and the bed material of said region. 